Titanium alloys are widely used in the high performance applications, such as gas turbine engines. For every application there is different balance of properties required. However, in gas turbine engine applications there is a common requirement for a good low cycle fatigue properties combined with a high fracture toughness and good tensile properties. Low crack nucleation and growth rates under cyclic loads are particularly important factors in rotating applications such as gas turbine disks which must be resistant to fatigue and, in the event of damage must be resistant to crack propagation. Should a crack form, the limiting size before rapid failure is set by the fracture toughness of the material. The larger the value the more crack tolerant the material. For disks operating at higher temperatures (&gt;500.degree. F.), good creep properties are required along with freedom from property degradation during long time exposures.
The Ti-6Al-2Sn-4Zr-6Mo alloy is potentially attractive for gas turbine engine applications because of its good tensile and low cycle fatigue properties. Unfortunately, to date, this alloy as conventionally processed has displayed relatively low fracture toughness and shows a significant reduction in low cycle fatigue properties when the surface of the article is even slightly damaged, i.e. scratched. These drawbacks have limited usage of this alloy in gas turbine engines.